TORONTO -- As Canada’s total number of confirmed cases of COVID-19 increases, health-care professionals are being inundated with questions about how the virus spreads, who’s at risk, and how people can protect themselves.

To sort through some of the noise, several doctors answered some of the most frequently asked questions about the ongoing pandemic.

Can the virus linger on surfaces or be transmitted through the air?

While the research is still in its early stages, the World Health Organization (WHO) says that preliminary evidence suggests the new coronavirus can persist on surfaces for a few hours or up to several days, but this might vary depending on conditions, such as the type of surface, humidity, and the environment.

As for whether the virus can be transmitted through the air, the WHO states that “the virus that causes COVID-19 is mainly transmitted through droplets generated when an infected person coughs, sneezes, or speaks" instead of through the air.

However, a new study from the U.S. National Institutes of Health and published in the “New England Journal of Medicine” has found that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19, was detectable in aerosols for up to three hours. The researchers discovered this by using a device to dispense an aerosol with duplicated microscopic droplets of the virus, which would be released by a cough or sneeze. The tests showed the virus in aerosols could still infect people for at least three hours.

The study also found the virus was viable, or contagious, for varying amounts of time on different surfaces. For copper it was viable for up to four hours, up to 24 hours on cardboard, and up to two to three days on plastic and stainless steel.

Dr. Isaac Bogoch, an infectious diseases specialist, said the study provided doctors with helpful guidance on the matter.

Can you contract COVID-19 more than once?

There have been media reports in China, Japan, and South Korea about individuals who had the virus and eventually tested negative for it and were released, only to test positive for it again a short time later.

Scientists in those countries have speculated that testing errors could be to blame, either for a false negative that said the patients were free of the virus or for the positive result that signalled its reoccurrence.

Dr. Iris Gorfinkel, a family physician and medical researcher, said it’s really too soon to know whether an individual can contract COVID-19 more than once, and how quickly that can happen.

“We actually don’t know. We don’t know how long-lasting the immunity is to it,” she told CTV’s Your Morning on March 16. “These viruses have the tendency to morph and change.”

In fact, it’s still not even clear if people develop an immediate immunity to COVID-19, as is typically the case with other virus strains, such as the flu.

“So just like any other virus, there’s the possibility that it could shift or drift. Just minor changes could change it from a once mild infection to a more severe infection,” she explained.

Infectious disease specialist Dr. Abdu Sharkawy said it’s “quite possible” for individuals who had COVID-19 to become infected again.

“One of the concerns we have is there may be a second wave of infection if our strategies for containment and for infection control are not good enough, and that's why it's really important for everybody to adopt a very consistent attitude and philosophy that we're in this for the long haul,” he told CTV’s Chief News Anchor and Senior Editor Lisa LaFlamme.

On April 11, the World Health Organization (WHO) told multiple media outlets they were investigating reports of recovered COVID-19 patients testing positive for the illness again after they initially tested negative.

However, the WHO said they still need more epidemiological data to draw any conclusions about the virus’ “shedding profile.”

Can you contract two viruses at the same time, such as new coronavirus and the flu?

While it’s still unclear if someone can contract the new coronavirus more than once, it is possible to have more than one different virus at the same time.

Dr. Isaac Bogoch said it’s absolutely possible for someone to have COVID-19 and a strain of the flu or another virus simultaneously.

“We sound like broken records in the medical and scientific community, but for the last two months we’ve been saying ‘We’ve got to prepare for this. We’ve got to prepare for this. Optimize your health,’” he told CTV’s Your Morning on March 20.

Bogoch said people should “optimize” their health by getting vaccinated for everything that they are eligible to be vaccinated for, such as influenza or bacterial pneumonias.

“It’s totally possible to have what’s called a co-infection and we know people who have multiple infections at the same time can have a worse outcome,” he said.

How do you know if you have a cold, the flu, or COVID-19?

Those who are infected with COVID-19 may have few to no symptoms, according to the Public Health Agency of Canada (PHAC). If symptoms are present, they can easily be mistaken for a common cold or the flu because of their similarities.

According to the health agency, the main symptoms of COVID-19 are fever, coughing, difficulty breathing, and pneumonia in both lungs. In severe cases, the illness can even result in death.

The World Health Organization lists additional symptoms that have been documented in some COVID-19 patients, including tiredness, aches and pains, sore throat, diarrhea, nausea and runny nose.

Gorfinkel said clinicians can’t distinguish between the illnesses based on symptoms alone. She said they can all present the same way, which is why the patient’s travel history or history of exposure to the virus is so important in determining whether someone might have COVID-19.

“We do not have the facilities or the tests to test absolutely everybody, so that history of travel if you’re basically otherwise well, that’s a critical part of it,” she explained.

Is losing your sense of smell or taste a sign of a minor case of COVID-19?

There have been reports of COVID-19 patients who lost their sense of smell and/or sense of taste, but they didn’t show any other symptoms of the disease.

Because research on the topic is still in its early stages, Dr. Isaac Bogoch said those symptoms alone are not enough to indicate someone has COVID-19.

“We don’t have all the answers yet,” he told CTV’s Your Morning on April 16. “But we're hearing more and more people who have disturbances in taste and smell and there's even some data that's emerging that says maybe about 25 to 30 per cent of people might have that, along with some other symptoms.”

Both the Public Health Agency of Canada and the World Health Organization have not included the loss of sense of smell and/or taste in their lists of symptoms.

Bogoch said it’s also important to remember that the loss of sense of smell and taste are common symptoms of many other upper respiratory viral infections.

“It’s not specific to COVID-19, but it certainly may be a component of this infection,” he said.

Can young people fall seriously ill?

While much of the attention about who is most vulnerable to COVID-19 has centred on the elderly and those with underlying medical conditions, it can also affect young people.

According to the latest PHAC data, as of April 15, COVID-19 patients under the age of 60 made up 65 per cent of Canada’s total cases, while those under the age of 50 made up 47 per cent of the total.

Dr. Isaac Bogoch said that everyone can be infected by the novel coronavirus and there’s always a risk that some people will have a more severe infection.

However, he said older people and those with underlying medical conditions still have a greater risk of a severe outcome than younger individuals.

“If we take a step back and look at the 30,000-foot view and look at who is more likely to get a severe infection, it is overwhelmingly those over the age of 60 and really, over the age of 80 years old,” he told CTV’s Your Morning on March 20.

Bogoch said the most important metric to look at when studying data about severe infections from this virus is death.

“If you get infected, you either live or you die, it sounds morbid, but I think that’s an extremely important distinction to make and if we look at death, it is overwhelmingly in those over 60 and disproportionately high in those over the age of 80,” he said.

Should you avoid Advil and other anti-inflammatories?

France’s health minister set off a wave of confusion when he warned that the use of ibuprofen could become an “aggravating factor” for infection in COVID-19 cases; however, the World Health Organization says there are no reports to support this claim.

In an official response, the WHO said it’s not recommending against the use of the common painkiller.

“We are also consulting with physicians treating COVID-19 patients and are not aware of reports of any negative effects of ibuprofen, beyond the usual known side-effects that limit its use in certain populations,” the WHO said in an update on March 18.

Bogoch agreed with the WHO, saying there is still not enough data on the subject.

“The short answer is we’re not entirely sure if this is going to do anything or not. It’s unlikely to have any effect whatsoever,” he told CTV’s Your Morning on March 19.

For individuals who suspect they may have COVID-19 and are suffering from a low-grade fever or another type of pain, Bogoch said they can take ibuprofen or other over-the-counter medications, such as acetaminophen.

The government agency concluded that there was insufficient evidence to avoid the drugs, but that “Acetaminophen continues to be a preferred first-line medication for symptom management due to the lower potential for side effects.”

If you have been in isolation because one person in your household is sick, do you have to continue to stay home for another two weeks if another person falls ill?

For people living in households with multiple residents, it may be difficult to avoid infecting each other. Dr. Isaac Bogoch says that if someone becomes sick with COVID-19, the best course of action is to call the local public health authority.

“It’s extremely important to call the local public health hotline to discuss the exact situation so they can give you very specific recommendations based on your unique setting,” he told CTV’s Your Morning.

In general, though, it appears the answer to that question may be a 'yes.' PHAC says that anyone who has been in contact with a suspected, probably or confirmed case of COVID-19 should self-isolate for 14 days, starting at the time of contact.

This approach was taken by Prime Minister Justin Trudeau, who entered self-isolation with his family after Sophie Gregoire Trudeau tested positive for the virus. Once his wife was given the all clear, the prime minister remained in isolation until it had been two weeks since their last contact before he went out in public again.

Who is getting tested?

There is a test that can detect the presence of COVID-19 in a patient, but jammed health-care systems mean many Canadians may make it through the pandemic without ever knowing if they had contracted the virus.

Canada does not have formal criteria for determining who should be tested, meaning guidelines vary from province to province. Health-care workers are generally advised to prioritize testing only those who are showing symptoms of COVID-19, particularly if they are in hospitals, long-term care homes or other institutional settings where they could easily spread the virus, as well as symptomatic travellers entering Canada.

Anyone who is showing symptoms of COVID-19 and is concerned they may have acquired the virus should contact their doctor or other primary health-care provider.

Can you contract the virus from passing people on the sidewalk?

While health officials have warned people to keep two metres apart from each other at all times to avoid spreading the virus, that’s not always possible in certain circumstances, such as in a narrow hallway or on the sidewalk.

Dr. Isaac Bogoch said that obviously people should try to avoid that situation, but there is a very low risk of transmission if it does.

“The risk of transmission for that second where people are passing within a two-metre radius of each other is almost zero per cent,” he told CTV’s Your Morning on April 16. “It's extraordinarily small.”

Even if one person is infected with COVID-19, Bogoch said it’s “extraordinarily unlikely” they will transmit it to someone passing them on the sidewalk.

Can you still gather with friends in small groups?

As physical distancing recommendations have evolved, it has become clear that authorities do not want anyone to get close to anyone from outside their household unless absolutely necessary.

"Stay home" has become the refrain from political and public health leaders seeking to flatten the curve of COVID-19 infections.

"Physical distancing is proven to be one of the most effective ways to reduce the spread of illness during an outbreak," PHAC says on its website, which recommends that all Canadians avoid "non-essential" gatherings.

Gorfinkel said people should aim to avoid all unnecessary contact with individuals to prevent further spread in their communities.

“Stop the spread because so many people have mild symptoms. That’s the problem,” she said. “They’re the source where the majority of cases are going to come from.”

Does taking vitamin C prevent or cure COVID-19?

While vitamin C has been praised as an immune-boosting vitamin, claims that it can be used to treat COVID-19 have not been proven.

Joe Schwarcz, director of McGill University’s Office for Science and Society, told CTVNews.ca that just because high doses of the vitamin are being used in clinical trials for COVID-19 treatments, it doesn’t mean there’s enough evidence to support its usage in the management of the disease.

“When you don't have any kind of effective medication, as we don't have for COVID-19, you pull out all the plugs and try everything,” he said.

“But this is a long way from people asking whether or not they should be taking huge doses of vitamin C to try to prevent infection by this virus. There is zero evidence for that."

In fact, social media posts encouraging people to increase their vitamin C intake may be more harmful than helpful if they’re taking too much.

Health Canada recommends 90 mg per day of vitamin C for the average adult male and 75 mg per day for the average woman. The tolerable upper intake level (UL), the highest daily intake likely to pose no risks, for adults is 2,000 mg per day.

Anyone who surpasses the recommended daily dose may be at risk of side effects, such as diarrhea, nausea, cramps, and an increased risk of kidney stones.

Do previous immunizations, such as the flu shot, help protect against COVID-19?

While there have been suggestions that a regular flu shot can help protect individuals against COVID-19, Bogoch said that’s not true.

“They do not protect against this particular infection. They do not protect against COVID-19,” he said.

However, Bogoch stressed that vaccinations such as the flu shot are still extremely important for optimizing health.

“We should be up to date on all our routine vaccinations, our pneumonia vaccines, our flu vaccines, our regular vaccines, so that we can ensure that our health is optimized in case we come down with an infection,” he said.

Should seniors and children be separated if they live in the same home?

While children appear to be less affected by the virus, elderly people and those with other medical issues are more at risk of suffering a severe outcome from a COVID-19 infection.

For families that have both seniors and young children living under the same roof, Bogoch said they should take care to separate them if anyone shows symptoms. However, he said that should be the case for anyone who is living with others and exhibits any symptoms, such as fever, coughing, and difficulty breathing.

“You just have to be very mindful if anyone has any symptoms whatsoever they should be separated,” he said.

How can caregivers protect themselves while helping someone with COVID-19 at home?

For people who are caring for a person who has been diagnosed with COVID-19, the Public Health Agency of Canada has a number of tips on how they can protect themselves while they provide care.

According to PHAC, only one healthy person should provide care to the individual with COVID-19, and that person should limit their contact with them as much as possible. They should also not share personal items with them, such as toothbrushes, towels, bed linen, utensils or electronic devices. The ill person should have their own bathroom, if possible. If not, they should put the toilet lid down every time before flushing.

Caregivers should wear a mask, disposable gloves, and eye protection when they’re in close proximity to the patient and never reuse the mask or gloves. They should also frequently wash their hands with soap and water, especially after contact with the sick individual.

When will things get back to normal?

In recent weeks, Canadian government and public health officials have been inundated with questions regarding how long restrictive measures to curb the spread of COVID-19 will be in place as people become fatigued with their new way of life.

Unfortunately, officials have only been able to offer vague timelines, suggesting that it could be “weeks” or even “months” before a sense of normalcy returns.

On April 15, Prime Minister Justin Trudeau said a key factor will be the availability of testing kits, which have been in short supply due to global shortages.

“When we are able to loosen the controls on social distancing and start to reopen our economy, massive, rapid testing on a very wide-scale basis will be an essential part of the vigilance we have to have,” he said.

Once the first wave of the epidemic has ebbed, Trudeau said they will have to be able to conduct widespread testing to ensure a second outbreak doesn’t occur.

Canada has already tested hundreds of thousands of people since the pandemic began, but health experts have warned that many more need to be done in order to weed out new outbreaks.

To address the shortage, Canada’s chief public health officer, Dr. Theresa Tam, said government and laboratory officials have been working on supply issues “every day” and have been focused on boosting domestic supplies so they’re not reliant on other countries for tests.

Will there be a second wave of infections?

With public health officials warning that Canadians must adhere to physical distancing policies in order to “flatten the curve” of infections, as Hong Kong and Singapore successfully did, other experts are expressing concerns about a “second wave” of infections after those regions experienced another spike in cases when they relaxed some of those measures.

Bogoch said that it’s possible Canada will experience a similar fate, if people aren’t diligent about maintaining isolation and physical distancing orders.

“If we take our foot off the gas pedal, when we start to lift some of these measures because we start to see the curve flattening, we have to be prepared that there might be a second spike in cases,” he explained.

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